<template>
  <div class="pagination">
    <button @click="$emit('change-pageNo',pageNo-1)" :disabled="pageNo===1">上一页</button>
    <button v-show="startAndEnd.start>1" @click="$emit('change-pageNo',1)">1</button>
    <span v-show="startAndEnd.start>2">...</span>

    <button v-for="(_,index) in (startAndEnd.end-startAndEnd.start+1)" :key="_" :class="{'active':startAndEnd.start + index===pageNo}" @click="$emit('change-pageNo',startAndEnd.start + index)">{{startAndEnd.start + index}}</button>

    <button v-show="startAndEnd.end<totalPage-1">···</button>
    <button v-show="startAndEnd.end<totalPage" @click="$emit('change-pageNo',totalPage)">{{totalPage}}</button>
    <button @click="$emit('change-pageNo',pageNo+1)" :disabled="pageNo===totalPage">下一页</button>

    <span>共 {{total}} 条</span>
  </div>
</template>

<script>
export default {
  name: 'Pagination',
  // props: ['total', 'pageNo', 'pageSize', 'continues','changePageNo'],
  props: ['total', 'pageNo', 'pageSize', 'continues'],
  computed: {
    // 1. 计算总页码
    totalPage() {
      // 总页码 = total / pageSize
      const { total, pageSize } = this
      return Math.ceil(total / pageSize)
    },
    // 2. 起始页和结束页
    startAndEnd() {
      // 这个起始页和结束页要根据当前页和连贯页来计算
      const { pageNo, continues, totalPage } = this
      let start, end
      // 判断第1种特殊情况 就是当连贯页码大于总页码时
      if (continues > totalPage) {
        start = 1 // 起始页
        end = totalPage // 结束 页
      } else {
        start = pageNo - (continues - 1) / 2
        end = pageNo + (continues - 1) / 2

        // 特殊情况二  如果根据当前页计算出来的起始页小于1的情况
        if (start < 1) {
          start = 1
          end = continues
        }

        // 特殊情况三 如果根据当前页计算出来的结束页大于了总页码 此时结束页就是总页码 再往前推连贯页码
        if (end > totalPage) {
          end = totalPage
          start = totalPage - continues + 1
        }
      }

      return { start, end }
    }
  },
  // methods:{
  //   sendPageNo(pageNo){
  //     // this.$emit() 这是触发自定义事件的

  //     this.changePageNo(pageNo)
  //   }
  // }
}
</script>

<style lang="less" scoped>
.pagination {
  text-align: center;
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #c81623;
      color: #fff;
    }
  }
  span {
    display: inline-block;
    line-height: 28px;
    font-size: 14px;
    color: gray;
    vertical-align: middle;
  }
}
</style>